A comparison of the immune response to PPD (O.6-6.5 mg/ml protein) and MT (mammalian tuberculin-USDA reference strength) using natural cases of primate tuberculosis is being determine. Results indicate the hypersensitivity response with MT is linear, increasing with the amount of protein present. The hypersensitivity response with PPD is not linear, plateauing at approximately 2.0 mg/ml. The response with MT was consistently of greater intensity than PPD using equivalent strengths above 0.6 mg/ml of protein. MT appears to be a better product for diagnosing tuberculosis in rhesus monkeys.